st/wgl: Don't export wglGetExtensionsStringARB.
st/wgl: Don't export wglGetExtensionsStringARB.

It's not exported by the official opengl32.dll neither.  Applications are
supposed to get it via wglGetProcAddress(), not GetProcAddress().

Cc: "10.4" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Reviewed-by: Roland Scheidegger <7d58aee419d6f9201d75517c885374dff5e7d848@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler